1. Field of the Invention
The present invention relates to a method for inspecting a mask.
2. Description of Related Art
Conventionally, as a method for inspecting a pattern (hereinafter referred to as mask pattern) on a mask or a reticle, adopted method is a method for detecting defects in such a way as to compare an inspection object data obtained by imaging a mask pattern with a design data (EB data) for an electron-beam direct drawing of the mask stored in a CAD.
Here, FIG. 12 shows the conventional and general mask inspection system. The mask inspection system 30 is comprised of an inspecting part 31, a converting part 32, a rendering part 33, a comparing part 34, a defect judging part 35 and a reviewing part 36.
The inspecting part 31 images a mask pattern of an inspection object, and produces the inspection object data of a bitmap form to send to a comparing part 34. The converting part 32 receives the EB data to convert to reference graphic data having the height, the width, and resolution and the like. The converting part 32 sends the converted reference graphic data to a rendering part 33. The rendering part 33 sequentially sends out the reference graphic data to the comparing part 34 while developing the reference graphic data into bit map form data depending on scan condition in the inspecting part 31.
The comparing part 34, as shown in FIG. 13, sequentially compares the inspection object data 37A received from the inspecting part 31 with the bit map data 38A received from the rendering part 38, and sends out the obtained difference value to a defect judging part 35. Within the drawings, reference numeral 37 indicates the mask pattern of the imaged inspection object, and reference numeral 38 indicates the reference graphic data. In the defect judging part 35, a threshold value to be determination reference to detect defect is set previously with respect to each sent difference value. The defect judging part 35 compares the difference value sent out from the comparing part 34 with the threshold value, followed by judging as being defect when the difference value is larger than the threshold value, and stores coordinate information of the defect and image data around the defect. Subsequently, defect judging part 35 send out the coordinate information and the image data of the detected defect about the predetermined inspection area to the reviewing area 36.
The reviewing part 36 displays an image screen on the basis of the coordinate information and the image data of the detected defect received from the defect judging part 35. Performed again is ascertainment with respect to classification of the defect or influence to the semiconductor chip, while referring to this image screen visually.
Meanwhile, even though size of the defect residing in the mask pattern is identical, it is known that there is difference in influence degree of the defect, depending on the position where the defect resides. However, in the conventional method for inspecting the mask using the above described mask inspection system, the whole inspection area of the mask is made to inspect with the same threshold value, therefore, there is a problem that the defect with small influence to the semiconductor chip affected is detected largely, so that it became the cause of lengthened TAT or the like in the semiconductor device.
In order to solve the above-described problem, for instance, in the pattern inspecting device in the Japanese Laid-Open Patent Publication NO. 2003-215059, a plurality of mask patterns are superposed and the area where the high accuracy inspection is required is set as a fine selected area comprising a superimposed area and its vicinity. The defect is judged while using different threshold value between the fine selected area and non-selected area.
Further, in the reticle appearance inspecting device of JP Patent Number 2776416, and the visual inspection and verification system of Japan National Patent Publication NO. 2001-516898, performed is wafer simulation to respective inspection object data and reference graphic data; and with respect to both data, obtained is wafer simulation data, which predicts a pattern transferred to the body to be transferred, on the basis of light intensity distribution, which aims at the body to be transferred of the pattern through the optical system of the stepper. Subsequently, performed operation is the defect detection, upon comparing the inspection object data with the wafer simulation data about the reference graphic data mutually.